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Study of protein-protein interactions in molecular epigenetics
No full textMolecular epigenetics describe the dynamic changes of chromatin structure, consisting of histones, associated proteins and DNA, which ensure a coordinated expression of genes during cellular differentiation. In the present PhD work, we have developed tools for the analysis of protein-protein interaction and the activity of protein (histone) lysine methyltransferases. We have also studied the substrate specificities of histone lysine methyltransferases (G9a and SET7/9) and the binding specificities of reading domains (PWWP domain of Dnmt3a and ADD domain of ATRX). DNA methylation patterns are set during embryogenesis by Dnmt3a and Dnmt3b enzymes. However, the mechanisms guiding these enzymes to their target regions are not well understood. In the present study, we have shown that PWWP domain of Dnmt3a recognizes the histone 3 lysine 36 trimethylation marks and we propose that this guides the enzyme to its target regions. ATRX is a chromatin remodeling protein, which is often found to be mutated in patients having alpha-thalassemia and mental retardation X-linked syndrome (ATR-X) syndrome. Nearly half of the disease causing mutations lies in the ADD domain of ATRX. However the function of this domain is unknown. We have shown that the ADD domain of ATRX recognizes histone 3 lysine 9 trimethylation marks. Our findings provided the functional clue about the heterochromatin localization of ATRX for the first time. We have developed a general method, which we designated as Absence of Interference approach for rapid mapping of protein-protein interaction sites by using Dnmt3a and Dnmt3L yeast two hybrid interaction pair as a model system. The method is well suited for high throughput applications as well
Atomic force microscopy on biomolecular building blocks : protein channels, peptides and vesicles
No full textThe Atomic Force Microscope (AFM) is an instrument which offers the opportunity to enter the nanometer-scale world of biophysics and nanotechnology. Within this thesis, the AFM is used to investigate and characterise polymer supported liposomes and engineered channel proteins for their applicability in nanocompartment systems as well as beta-sheet forming polypeptides with respect to their possible application in nanoelectronics. The molecular systems of interest are polymer supported liposomes, which we characterise, as well as the transmembrane protein FhuA. Therefore, a protein purification process is established and protein crystallisation experiments are performed. Additionally, high resolution measurements on the test system bacteriorhodopsin are carried out in order to optimise imaging conditions. Furthermore, we investigate different types of artificial polypeptides which self-assemble into beta-sheets. The resulting beta-sheets are characterised and tested for their suitability as building blocks for nanoelectronic purposes. For these different research foci, suitable sample preparation methods are developed and the measurement settings are optimised. The quality of the results is directly influenced by the choice of substrate, the immobilisation method, the measurement conditions (air, solution, buffer composition) and the measurement modus (tapping mode, contact mode) as well as by the nature of the investigated object itself
The relationship between emotional experience, social context, and the face : an investigation of process underlying facial activity
No full textThis dissertation investigates underlying processes and mechanisms of the relationship between emotion, facial activity, and social context. The theoretical framework derives from two contrasting views of facial activity, Ekman's neuro-cultural model (e.g., Ekman & Friesen, 1971), and Fridlund's (1991) behavioral ecology. Evidence presented by either view has been difficult to account for by the other. Furthermore, the exact nature of automatic and controlled processes has remained elusive. An integrative social cognition approach is employed to shed new light on the controversy. In experiments 2-1 and 2-2, an implicit association test (IAT) showed associations between the concepts of "friends" vs. "strangers" and being emotionally expressive ("show") vs. attenuating ("hide"). Furthermore, the type of film watched before performing the IAT modulated the size of the effect, albeit in an unexpected direction. In experiment 3, participants were primed with "I", "We", or "They" before watching funny films. "We"-priming led to significantly higher levels of activity at the Orbicularis Oculi site compared to "They"-priming. Experiments 4-1 and 4-2 investigated effects of the imagined of physical presence of friends or strangers and resulting conflicts between automatic and controlled processes. Correlations between self reports and smiling showed diverging patterns for friends and strangers in experiment 4-1, and interference between automatic and controlled processes in the presence of friends in experiment 4-2. Despite conscious goals to display their enjoyment of funny films via Corrugator Supercilii activation, participants showed less Corrugator Supercilii activity when in the presence of a friend. Together, the present results suggest automatic processes that link characteristics of the social context with fundamentally different types of facial behavior. The findings are discussed in relation to the theoretical framework and an evolutionary psychology perspective
Transition metal containing silico- and germanotungstates
No full textThis work focuses on the interaction of the versatile dilacunary silicotungstate unit with different metal cations leading to novel compounds interesting for magnetic and catalytic applications. Also this work reports two new lanthanide containing polytungstates, a sandwich type silicotungstate and a dimeric-pentameric germanotungstate. The 15-cobalt-substituted polyoxotungstate (1) has a core of nine CoII ions encapsulated by three unprecedented fragments and two Chloro ligands. The 6-cobalt-substituted silicotungstate (2) contains three cobalt ions which are encapsulated between an unprecedented fragment and a lacunary unit. The new, monometal substituted silicotungstates (3-5) are composed of two units fused on one side via two W-O-W' bridges and on the other side by an octahedrally coordinated transition metal fragment. The trimeric species (6) consists of three units linked by an unprecedented Zr6 cluster with C1 point group symmetry. The dimeric species (7) consists of two units sandwiching a Zr4 cluster and has also C1 symmetry. The unprecedented peroxo-zirconium(IV) containing silicotungstate (8) comprises a cyclic 6-peroxo-6-zirconium core stabilized by three decatungstosilicate units and represents the first structurally characterized Zr-peroxo POM with side-on, bridging peroxo units. The mono-lanthanide containing polyanions (9-16) have also been syntesized. Larger Ln3+ ions appear to favor an R,R (or S,S) configuration (point group C2) of the Keggin units, with an increasing amount of R,S (or S,R) configuration (point group C1) found in the solid state as the Ln3+ ion decreases in size. Finally, The gigantic 20-cerium(III) containing 100-tungstogermanate (17) represents the first lanthanide substituted tungstogermanate and it is one of the largest polytungstates reported to date
Notes on an Entropy-like Method for Robust Parameter Identification
No full textThis reports describes the basic ideas behind a novel parameter identification algorithm exhibiting high robustness with respect to outlying data. The algorithm consists in minimizing an entropy-like cost function of the identification residuals. Robustness to outliers is obtained as a consequence of the fact that the used cost function rewards unevenly distributed residuals rather than some kind of weighted mean square error (MSE). In particular residuals are normalized to the MSE and the minimization of the devised entropy-like function rewards the presence of a majority of low relative errors and a minority of large ones, rather than a least MSE that tends to level out residuals hence often hiding outliers. A preliminary theoretical analysis of the algorithm is reported together with experimental results to demonstrate the method. This work builds on ideas initially elaborated in 1999 and extended only in the Summer of 2006 during a research visit at the IUB International University Bremen (now Jacobs University Bremen gGmbH). The author is deeply grateful to Prof. Herbert Jaeger of the Jacobs University Bremen for his precious technical help and for having made this work possible
Organic Transistors Prepared by Self-Assembly and Printing Processes
No full textFlexible and lightweight electronics realized on large areas has gained considerable attention in recent years. The interest is particularly generated by the wide demand in low cost large area displays, smart cards and radio frequency identification tags (RFID) and the like. Such electronic devices can only be realized at low cost if novel material systems and new ways of fabricating the devices and systems are developed. Organic semiconductors are a very promising material system used for such applications. Organic materials and organic electronic device components can be printed, which allows for large area processing at low fabrication cost. Thus, organic semiconductors and printing methods are required to attain the desired low cost, and/or large electronic devices. In this study, organic thin film transistors (TFTs), which are key elements of organic electronic devices like RFID tags, flexible display media and smart tags are investigated. Pentacene, an organic semiconductor, is investigated as active materials in thin film transistors. The electrodes of the transistors are fabricated by microcontact printing. Microcontact printing is a method in which a self-assembled monolayer is used to functionalize, modify or pattern surfaces or films. In the study, new microcontact printing based methods were developed, which use self-assembled monolayer as dewetting agent. Next, the printing method was applied to fabricate pentacene TFTs. Furthermore, the device performance of the TFTs prepared by printing methods are studied and compared with transistors prepared by conventional optical lithography. Finally, the environmental and electrical stability the pentacene transistor was studied
Scaling limits and Megahertz operation in thiophene-based field effect transistors
No full textTo achieve high performance organic field effect transistors (OFETs) with enhanced currents, high switching speeds and improved integration density the channel length L of the transistors is downscaled to the sub-micrometer regime. The influence of the semiconductor thickness on the electrical performance, especially on the charge carrier mobility [Mu], is analyzed. High-mobility oligo- and polythiophenes are used as semiconductor, which combine the advantages of highly ordered growth with processibility from solution. To test for better device properties in these bottom contact devices, the conjugation length of the organic semiconductor is varied. Special focus hereby lies on the contact resistance of the transistors. Devices with optimized parameters exhibit high switching frequencies beyond 2 MHz. At the time of publication, these are the fastest polymer OFETs reported in literature
Biochemical characterization of the mammalian Dnmt3 family of DNA methyltransferases
No full textAll human cells carry the same genetic information, yet they follow different developmental pathways, which need to be realized with precision. Epigenetic regulatory mechanisms exist to ensure a coordinated expression of genes during cellular differentiation. These include modification of chromatin state and addition of methyl groups to DNA; both act in concert to regulate gene expression. However, whereas the role of these modifications has been studied in details, mechanisms leading to their establishment in specific regions of the mammalian genome remain poorly understood. The focus of this study was to elucidate mechanisms contributing to the specificity and targeting of DNA methylation by the mammalian Dnmt3 family of DNA methyltransferases (MTases). First, we explored the inherent properties of Dnmt3 enzymes, which might contribute to their specificity. We discovered a new level of specificity displayed by Dnmt3a (and Dnmt3a/Dnmt3L complex). We further demonstrated that Dnmt3a (and Dnmt3a/Dnmt3L complex) form nucleoprotein filaments on DNA in a cooperative manner and that the multimerization of Dnmt3a is required for its localization to pericetromeric heterochromatin. Finally, we contributed to the elucidation of the mechanism regulating the activity of three estradiol-responsive genes
Synthesis, structure and properties of multi-transition metal-substituted polyoxotungstates
No full textPolyoxometalates (POMs) are inorganic metal-oxygen clusters with an enormous structural and compositional variety. To date no transition metal derivatives of the crown-shaped 48-tungsto-8-phosphate [H7P8W48O184]33- (P8W48) or its half unit [H6P4W24O94]12- (P4W24) are known. Therefore, we decided to perform a systematic study on the interaction of different transition metal ions with P8W48 and P4W24 in aqueous, acidic medium.
Chapter 1 contains an extensive introduction to the class of POMs.
Chapter 2 describes the synthetic procedures for the lacunary POM precursors and the experimental techniques used for characterizing the products.
Chapter 3 describes the synthesis and structural characterization of the wheel-shaped Cu20 tungstophosphate [Cu20Cl(OH)24(H2O)12(P8W48O184)]25-. The Cu2+ containing polyanion is composed of a cyclic P8W48 template fragment with a highly symmetrical, cationic {Cu20(OH)24}16+ cluster guest.
Chapter 4 describes the synthesis and structural characterization of [P8W48O184Fe16(OH)28(H2O)4]20- which is composed of a 16 metal center iron-oxide nanocluster incorporated in the cyclic P8W48 template wheel.
Chapter 5 describes the synthesis and characterization of an organoruthenium derivative of the cyclic P8W48 anion: [{K(H2O)}3{Ru(-pcymene)(H2O)}4P8W49O186(H2O)2]27-.
Chapter 6 describes the synthesis and characterization of [Li(H2O)K4(H2O)3{(UO2)4(O2)4(H2O)2}2(PO3OH)2P6W36O136]25- which represents a uranium–peroxo derivative of the hitherto unknown “P6W36” Wells–Dawson ion.
Chapter 7 describes the facile incorporation of platinum(IV) into polyoxometalate frameworks by the preparation of [H2PtIVV9O28]5- and its characterization by 195Pt and 51V NMR spectroscopy.
Chapter 8 describes collaborative projects on the electrochemical, electrocatalytic, magnetic and EPR properties of some of the above mentioned compounds.
Chapter 9 describes unpublished and incomplete results
Personality development in older age : a quasi-experimental, longitudinal field study
No full textEmbedded in the general conceptual agenda of lifespan developmental psychology and its emphasis on the potential of individual development into old age, the central objective of the present study was to investigate whether participation in a volunteer training program can promote personality development in older age. The program "Erfahrungswissen für Initiativen" was developed by the German Federal Ministry of Family, Seniors, Women and Youth. The aim of the volunteer training program (VTP) was to encourage volunteers to develop a new role identity in the context of civic engagement by developing and initiating their own personal volunteering project. To investigate the impact of the VTP on personality development, participants of the VTP and an active control group of volunteers were assessed three times, before the VTP (T1), after the VTP (T2) and one year later as a follow-up assessment (T3). In addition, a second control group consisting of inactive, non-volunteers were recruited to validate the comparability of the active control group. The results showed that participation in the VTP increased personality adjustment by increasing life satisfaction and by decreasing negative affect and neuroticism from T1 to T2. Even though life satisfaction decreased again, negative affect and neuroticism remained decreased from T2 to T3. In accordance with the proposition that for personality growth to occur it takes a very special combination of personal and contextual factors, only participants of the VTP with high internal control beliefs increased in "personal growth" and "openness to experience" from T1 to T2. From T2 to T3 levels on "personal growth" remained elevated, while "openness to experience" increased even further. Taken together, the study presents an initial piece of evidence that by giving elderly the opportunity to participate in a meaningful way in society personality development is possible, even in older age